When I was running Gooch's Corals a few years back we used nothing but rubble early on. Let me tell you it was a pain in the bottom. I had frags constantly getting knocked into each other, falling and getting lost. I had tanks just loaded with rubble. Some of you might remember that. Rubble took up far more space than I had intended. Which meant setting up more tanks as I grew. We experimented with concrete and plastic with mixed to poor results. It wasn't until I was just about ready to give up the farm that we started playing with ceramics. By then other farmers were using aragonite plugs and it wasn't that I particularly liked the look. But I liked that I only got the coral. Less chance of parasites hidden deep inthe rock either.
I had decided to close shop and put up a 360+ gallon tank and just enjoy it. The goal of the tank was to be as close to 100% aquacultured as possible. I built an aquascape out of 100% ceramic. No liverock was going to be used. Why? Because I still feel liverock is over rated. While I was building the structure I strategically placed holes in the rockwork to place aquacultured corals on plugs. After seeing these aragonite plugs I was shocked at how brittle and crappy they were. They would just crumble with little force. So I rolled out a couple plugs for myself. Of course I was doing a build of my progress at the time. Soon private message after private message came and I was getting tons of requests for plugs. I never dreamed that many people wanted to use plugs. It got to the point that I could no longer work on my own tank. I had to sell the tank, it never saw a drop of water, because I needed more space to make plugs. This is the display tank at Reefs. To date we have made over 300,000 plugs and disks. And I believe we are one of the smaller plug makers. I had never ever planned to do another business and trust me this one almost cost me my wife. She still hates it and would probably more than happy if I ever pulled the plug on it. But she knows now I am always going to do something. Better in the shop and not in the bars.
Why do more and more people switch to plugs and disks? I really don't think there is one good answer. I think for me getting a coral on a plug tells me the grower is actively into propagation and not just chopping up wild colonies and selling them three days after they come in. I like to see that plug encrusting. I know the grower has at least had it in a system capable of growing coral. And as long as I have been in this hobby that is not always the case. How many LFS have you been in where you felt the need to save a coral or fish. I don't do that anymore. Frag plugs also take up much less space and can be stored dry. They are relatively inexpensive when you compare them to other things. You can get 50 plugs for about $15. If I had say a 40 breeder set up I can probably keep a couple hundred frags growing out at one time. I doubt I could do half that with rubble. I know for a fact today I could probably grow out almost as many frags in two 40 breeders as I did in my entire shop using rubble. This saves the hobbyist money by maximizing the space they have to work with.
And the argument that frag plugs are ugly and hard to use. Well, Yes they are ugly. But they also grow over quickly and after awhile you do not notice them. You do have to glue or epoxy the plug into place at times but you need to do this with rubble as well. Sometimes you can get lucky and wedge it into a hole in the rock. I designed ours so that the stem is easy to remove flush. The disk stem can be snapped off with just a little finger pressure or a bone cutters. The plug might take a bone cutter but I have no issues snapping them off most of the time with my fingers. A plug is less intrusive to your rockwork. You just glue it into place and watch it grow. Depending on the rubble it doesn't always fit well into the rockwork. Early on I probably spent more time picking up corals on rock than anything else.
Now we took things a step further with the Frag Stations and our other products. We do our best to try to make propagation easier and more attractive for everyone. In my 65 gallon reef I can grow out 65 frags on plugs at one time. No exra tank, lighting, pumps or equipment. I do not sell coral anymore but if I wanted to I could have a nice little low cost operation where I could sell 65 to 100 frags a month right out of my display tank once it matures. Growing in the same contitions as the mother colony at a fraction of the cost of having a frag tank.
But in the end it is a personal choice. Plugs for me are just easier.